1. Field of the Invention
The present invention generally relates to monitoring of acute decompensated heart failure in subjects having an implantable medical device.
2. Description of the Prior Art
The heart is an essential organ in humans and most animals, pumping blood throughout the human/animal body. As a consequence, it is fundamentally important that the mechanical pumping properties of the heart operate correctly.
There are several diseases and conditions that negatively affect these mechanical properties of the heart. A severe such condition is acute decompensated heart failure (ADHF). This form of heart failure is characterized by the sudden inability of the heart to pump efficiently. However it is though not cardiac arrest because the heart does not stop though the heart pumping action significantly deteriorates.
The inability of the failing heart to pump blood in a forward direction creates a relative hypovolemic state known as arterial underfilling. As a response, several neurohormonal factors become activated to maintain euvolemia by causing fluid retention, vasoconstriction, or both. In the patient without heart failure, this response terminates once fluid volume has been restored. However, the activity of these systems remains chronically elevated in the patient with heart failure, thus contributing to the systemic and pulmonary congestion that are hallmarks of the disorder despite compensatory elevations in endogenous brain natriuretic peptide (BNP) levels. Neurohormonal activation also stimulates detrimental activation of pro-inflammatory cytokines and mediators of myocyte apoptosis. As reported in “Acute Decompensated Heart Failure: A Contemporary Approach to Pharmacotherapeutic Management,” McBride et al, Pharmacotherapy 23(8), pp. 997-1020 (2003), elevations of many of the neurohormones and immunomodulators observed in patients with ADHF have been associated with a worsening of heart failure symptoms and a decline in the prognosis of the patients. Although these hormones are elevated in patients with compensated heart failure, their elevation can precipitate an episode of ADHF if they are not adequately suppressed by therapy.
Approximately 4.9 million people in the U.S. were diagnosed with ADHF in 2003. ADHF is the single most expensive hospital admission diagnosis according to the Center for Medicare and Medicaid Administration, with more than $3.6 billon spent in 1998 alone.
The success in treating ADHF patients and reducing the enormous cost associated with ADHF, is an early patient diagnosis. Today ADHF diagnosis is mainly limited to patient's history, physical examination, chest X-ray examination and laboratory tests. Characteristic of this prior art ADHF diagnosis is that it is time-consuming and cumbersome, often requiring dedicated X-ray and imaging facilities in addition to separate laboratory testing.